This invention relates to sewing machine controls in general and, in particular, to a new and useful speed control device for the motor of a home sewing machine.
The hitherto known devices of this kind have the disadvantage that the resultant sewing machine control is imperfect in the lower speed range. It is precisely in the lower speed range, however, that a great torque must be available to assure a large needle piercing power at a low number of sewing machine stitches.
A home sewing machine is known from U.S. Pat. No. 3,503,352, which has a motor with two circuits, the first circuit being intended for normal driving with variable speed and the second for driving at a reduced speed. The second circuit becomes effective when the variable resistor of the first circuit, built into the foot starter, is turned off completely by setting back the starter rocker. It serves the purpose of stopping the sewing machine in a predetermined needle position, usually the high needle position. To accomplish this, the second circuit is turned off in a predetermined position.
The known arrangement has the disadvantage that the operator, particularly at the end of a sewing operation with the machine already stopped, can still keep the variable resistor operative by operating the starter rocker slightly. Since, in its uppermost setting range, the resistor's resistance usually exceeds the amount of resistance required to start the motor, which amount is determined by the frictional drag occurring in the machine or, while sewing, the sewing machine usually does not start in this setting range.
If the operator then turns off the variable resistor by setting the starter rocker back completely, either accidentally or intentionally, the second control circuit is turned on, and the machine is brought into the predetermined stopping position. This places the operator in great danger, particularly if this happens during a manipulation of materials on the sewing machine.